The invention relates to an exhaust system for an internal combustion engine.
EP 0 417 412 A2 discloses an exhaust system in which, in addition to a main catalytic converter, there is in each exhaust conduit a start-up catalytic converter arranged near the engine in an annular duct surrounding the exhaust conduit. At low exhaust temperatures, the exhaust pipe is closed in the region of the annular duct by a butterfly valve, whereby the exhaust gases are discharged via the start-up catalytic converter which is activated very quickly.
The disadvantages of this arrangement are that, on the one hand, the downstream main catalytic converter requires a relatively long preheating phase before it reaches the operating temperature and, on the other hand, the start-up catalytic converter and the butterfly valve are subject to very high thermal loads.
It is the object of the invention, in an exhaust system of this type with at least one start-up catalytic converter arranged near the engine and a main catalytic converter arranged remote from the engine, to relieve the start-up catalytic converter of thermal loads at high exhaust gas temperatures but to feed the exhaust gases to the main catalytic converter at as high a temperature level as possible.